The present invention relates to a gas seal and more particularly is concerned with a bilaterally rotatable gas seal utilized for a shaft sealing device for a rotation shaft.
One example of a gas seal of this type is Shown in FIG. 7A, in which slide members 100 and 101 on the fixed side and the rotating side, respectively, are disposed and the slide member 101 on the rotating side has a sliding surface 101A on which grooves 102 are formed for generating hydrodynamic floating force between the sliding surfaces of both slide members 100 and 101.
The slide member 100 on the fixed side 100 is supported by a spring 103, and in usual, the slide member 100 is raised by involving gas G between the sliding surfaces 100A and 101A of both the sliding members 100 and 101, and a gas space having a width h of 1 to 10 micron is caused between the slide members 100 and 101, which are sealed with an allowable slight leakage.
As shown in FIGS. 7B to 7E, a spiral groove 102A and radial grooves 102B are shown as examples of the floating force generation grooves 102. In the example of the spiral groove 102A, the gas G flows inside along the inner periphery by the rotation of the slide member to thereby cause a floating force, and on the other hand, in the example of the radial groove 102B, the gas G is discharged together with the generation of the floating force by centrifugal force caused by the wide groove width because the grooves are opened on an outer diameter side, and particularly, under high speed and low pressure condition, the centrifugal force is large and the gas pushing force is weak, so that the floating force is weak, thus stable sealing performance is not expected.
Furthermore, FIGS. 7F and 7G show another example in which a T-shaped groove 102C is formed as the floating force generation groove, and in such example of the T-shaped groove 102C, more increased floating force can be obtained in comparison with the example of the raidal groove, but the floating force is less than that of the example of the spiral groove. However, the gas seal device having a slide member provided with the spiral groove is of a uni-directionally, not bilaterally, rotatable gas seal device.